The present invention relates broadly to sensors for the monitoring of flow rates or flow conditions within pressurized fluid channels and, more particularly, to the limitation of flow valves when the flow rate exceeds a given level at a particular location within the pressurized channel.
Flow rate and flow condition limit valves are commonly employed as safety devices in pressurized fluid distribution systems to isolate fluid sources from any ruptures or breaches, thereby minimizing the loss of pressurized fluid. Safety-designed fluid transport systems using pressurized gases or liquids that are toxic, corrosive, radioactive, or explosive, employ flow limit valves to minimize exposure to these hazardous elements in the event of an accident or other undesirable event.
Flow limit valves allow fluid flow up to a predetermined limiting flow rate; the flow rate is determined by the difference between the upstream (inlet) supply pressure and the downstream (outlet) pressure. During normal operation, the pressure differential across the valve establishes a flow rate of the valve that is less than or equal to the limiting flow rate. A rupture in the downstream distribution system will cause a reduction in the downstream pressure and, hence, an increase of pressure differential across the valve. This increased pressure differential corresponds to a flow rate through the valve that may exceed the limiting flow rate.
To limit the flow rate through the valve to a predetermined limit, there has, in the prior art, been employed a piston, or similar device, which provides blockage of the flow path when the pressure differential exceeds that corresponding to the limiting flow rate. During this condition, all flow through the valve is blocked while the pressure differential is lowered to repair the rupture, thereby permitting the piston to be re-set to its original position.
As an alternative to complete blockage of the valve to limit flow rate, there may be provided, as in the below-set forth disclosure, a by-pass channel the effect of which is to reduce the flow rate below the limit value.
A typical prior art flow limit valve includes a primary flow path, through an orifice from an inlet port, to an outlet port. A movable piston is provided to close the primary flow path when the pressure differential across the orifice exceeds a certain value. Fluid from the inlet and outlet sides of the orifice is ported to opposite sides of the piston. The outlet pressure, assisted by a spring, tends to move the piston to an open position, which permits fluid to flow through the valve, and the inlet pressure tends to move the piston to a closed position, which prevents fluid flow. The spring and the piston are designed such that any pressure differential greater than the pressure differential that corresponds to the limiting flow rate, allows the inlet pressure to overcome the outlet pressure and the spring force to move the piston to the closed position. To reset this flow limit valve, a bypass valve is opened, and fluid flows through a secondary flow path to equalize the pressure on each side of the piston, thereby allowing the spring to move the piston to the open position.
Certain known valves use a third flow path with an integrated valve to bypass the shut-off piston for providing adjustment of the flow limit. Flow limit valves of these types are expensive to manufacture and difficult to purge due to the multiple flow paths and bypass valves involved. Also, the flow rate through a flow limit valve should be proportional to the pressure differential up to the limiting value of the flow rate, and should sharply fall to zero when the limiting valve is exceeded. However, spring-biased flow limit valves allow a flow rate that is proportional to the pressure differential up to the point where the piston begins to compress the spring and to move from the open position to the closed position, but does not provide a sharp closure because of the additional pressure differential necessary to further compress the spring and complete the movement of the piston from the open position to the closed position.
The instant invention seeks to overcome the above-set forth problems in the prior art through the use of repelling magnets in lieu of springs and, as well, an externally adjustable member by which the degree of magnetic repulsion and, thereby, the flow limit levels of the valve may be sensed and then adjusted.
Prior art references known to the inventor in the subject art area are U.S. Pat. Nos. 4,210,174 (1980) to Eross entitled Positive Pressure Valves; and No. 4,624,443 (1986) to Eidsmore entitled Fluid Flow Control Valve.
The above-recited reference to Eross is not a sensor; although magnetic means are provided, it is intended only to control and monitor pressure levels, not flow levels, this being a particularly important distinction in the instant art area. The patent to Eidsmore employs springs in combination with a complex structure of magnets and, as well, does not provide a by-pass capability. Further, its primary concern is that of monitoring pressure drops, not flow rate changes as is the concern of the inventor herein.